1) RFC2518's special handling of "lock null" resources will be
deprecated in RFC2518bis. So absolutely no need to worry about special
cases. Treat them as locks on empty resources (as if a PUT with no body
was done immediately before the LOCK).

2) That being said; the parent directory will only be deletable if you
submit the lock token with the DELETE request (both with standard
locking semantics and the special cases defined by RFC2518 for "lock
null" resources).